1. Field of the Invention
The present invention relates to a fuel cell in which fuel gas and oxidizing agent gas are used as reaction gases and also relates to a separator for the fuel cell and a manufacturing method of the separator.
2. Technical Background
Disclosed in Japanese Patent Laid-open Publication Nos. 8-507402 and 11-126621 is a fuel cell in which fuel gas and oxidizing agent gas are used as reaction gases. The fuel cell is composed of a plurality of cell function assemblies arranged in parallel and fastened by a plurality of mounting bolts through a pair of spaced current-collecting plates made of conductive material and a pair of spaced insulation support plates. The cell function assemblies each are in the form of a cell function assembly 10a as shown in FIG. 1. The cell function assembly 10a is composed of a set of spaced solid electrolytic membranes 14, two pairs of electrode plates 13a, 13b adhered to opposite surfaces of each solid electrolytic membrane 14, and a set of three separators 15 assembled to retain the solid electrolytic membranes 14 in position. The separators 15 are adhered to one another by means of an adhesive agent such as epoxy resin and fastened by mounting bolts through a pair of spaced current-collecting plates 11 and a pair of spaced insulation support plates 12.
In the fuel cell, the separator 15 is, in general, made of conductive material such as carbon resistant to oxidation-reduction atmosphere caused by chemical reaction of the reaction gases. The separators 15 are arranged to form reaction chambers R1, R2 for chemical reaction of the reaction gases in the cell function assembly 10a and to derive an electric power generated at the electrode plates 13a, 13b to the exterior. The separator 15 has a flat plate portion 15a forming the reaction chambers R1, R2 and a plurality of columnar projections 15b in contact with the electrode plates 13a, 13b. 
For manufacture of the separator 15, an expensive carbon block of predetermined thickness is used as a material of the separator 15. In a manufacturing process of the separator 15, the carbon block is machined by cutting at one side or both sides thereof to form the columnar projections 15b of separator 15. As the cutting process of the carbon block is time-consuming, the manufacturing cost of the separator 15 becomes very expensive, for example, several ten thousand yen per one piece. Due to such expensive manufacturing cost, use of this kind of fuel cell may not be widely popularized.
As the separator 15 in the fuel cell is conductive in its entirety, the components of cell function assembly 10a are electrically connected. For this reason, an electric power may not be generated at different voltages in the fuel cell.
It is, therefore, a primary object of the present invention to reduce the manufacturing cost of the separator as lower as possible for providing this kind of fuel cells at a low cost.
A secondary object of the present invention is to provide this kind of fuel cells capable of generating an electric power at different voltages in a range from a high voltage to a low voltage.